ESD device with salicide layer isolated by shallow trench isolation for saving one salicide block photomask

ABSTRACT

A electrostatic discharge (ESD) device with salicide layers isolated by a shallow trench isolation in order to save one salicide block photomask. A shallow trench isolation is formed in drain region to isolate a portion of the drain region, so that the drain region is partitioned into two parts. A salicide layer is formed on the drain region. Since the salicide layer is not formed on the shallow trench isolation, without using an additional photomask, the salicide layer on the drain region is partitioned into two parts. The effect of the local thermal energy occurring to drain junction upon the contact metal of the drain region is eliminated.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationSerial No. 89123687, filed Nov. 9, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a semiconductor device comprising asalicide layer. More particularly, this invention relates toself-aligned silicide (salicide) layers isolated by a shallow trenchisolation for the purpose of saving one salicide block photomask.

2. Description of the Related Art

During or after the fabrication process of an integrated circuit (IC)such as the dynamic random access memory (DRAM) and the static randomaccess memory (SRAM), the electrostatic discharge is a major reason forthe damage of the integrated circuit. For example, when one walks on acarpet in the environment with a high relative humidity (RH), hundredsto thousands of electrostatic voltages are carried. When the relativehumidity is low, the electrostatic voltage as high as tens of thousandsvolts can be carried. When these electrostatic charges are in contactwith a chip, a discharge is very like to damage the chip to cause thedevice failure.

FIG. 1 shows an electrostatic discharge (ESD) device structure with asalicide layer isolated by a salicide block. The ESD device structurecomprises a P type substrate 10, a drain region 12, a first sourceregion 14, a second source region 16, a first gate 18 and a second gate20. The drain region 12, the first source region 14, the second sourceregion 16 are formed by doping N+ type ions into the P type substrate10. The first and second gates 18 and 20 are located between the drainregion 12 and the first source region 14, and between the first sourceregion 14 and the second source region 16, respectively. On the surfacesof the drain region 12, the first and second source regions 14 and 16,and the first and second gates 18 and 20, a salicide layer 22 is formed.A metal layer 24 is further formed to connect the drain region 12, thefirst source region 14 and the second source region 16.

To enhance the capability of the electrostatic discharge, a salicideblock 26 is formed surrounding the salicide layer 22 on the drain region12, so that the salicide layer 22 on the drain region 12 is isolatedfrom the first and second gates 18 and 20. As a result, the effect ofthe local heating occurring at the drain junction upon the contact metalof the drain region can be eliminated. However, the formation of thesalicide block 26 requires an additional photomask, so that thefabrication cost and time are raised.

SUMMARY OF THE INVENTION

The invention provides a electrostatic discharge (ESD) device with asalicide layer isolated by a shallow trench isolation instead of beingisolated by the salicide block photomask to eliminate the effect oflocal heating in the drain junction upon the metal contact.

The ESD device comprises a P type substrate, in which an N well isformed. A gate is formed in the P type substrate out of the N well. Ashallow trench isolation is formed in the N well to isolate a portion ofthe N well. A source region is formed in the P type substrate next tothe gate, and a first drain region is formed in the junction of the Ptype substrate and the N well between shallow trench isolation and thegate. A second drain region is formed in the portion of the N wellisolated by the shallow trench isolation. A salicide layer is formed onthe gate, the source region, the first drain region and the second drainregion, while the salicide layer on the second drain region is isolatedfrom that on the first drain region by the shallow trench isolation.

In another embodiment of the invention, in a P type substrate on whichan N well is formed, a P well is further formed in the N well. A gate isformed on the N well out of the P well. A shallow trench isolation isformed in the P well to isolate a central portion of the P well. Asource region is formed in the N well and a first drain region is formedin the junction of the P well and the N well between the shallow trenchisolation and the gate. A second drain region is formed in the portionof the P well isolated by the shallow trench isolation. A salicide layeris formed on the source region, the gate, the first drain region and thesecond drain region, while the salicide layer on the second drain regionis isolated from that on the second drain region by the shallow trenchisolation.

Both the foregoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an ESD device structure with a salicide layer isolated by asalicide block,

FIG. 2 is an ESD device structure with a salicide layer isolated by ashallow trench isolation according to the invention; and

FIG. 3 shows another embodiment of the salicide layer isolated by ashallow trench isolation according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the conventional ESD device structure, a salicide layer is isolatedby a salicide block to eliminate the effect of local heat generating atthe drain region on the drain contact metal. The formation of thesalicide block requires an additional photomask, and thus, to cause araise in fabrication cost and time consumption. The invention providessalicide layer isolated by a shallow trench isolation. As the salicidelayer is not formed on the shallow trench isolation, so the additionalphotomask is not required.

In FIG. 2, the first embodiment of the invention is shown. On a P typesubstrate 30, an N well 32, source regions 34, gates 36, first drainregions 38, shallow trench isolations 40 and a second drain region 42are formed.

The N well 32 is formed in the P type substrate 30. In this embodiment,from a cross sectional view as shown in FIG. 2, two gates 36 are formedon the P type substrate 30 at two sides the N well 32. Two shallowtrench isolations 40 are formed in the N well 32. N type ions implantedinto the P type substrate 30, so as to form the source regions 34, whichdo not overlap with the N well 32. A salicide layer 46 is also formed onthe source region 34. A gate 36 with a salicide layer 48 thereon isformed on the P substrate 30 between the source region 34 and the firstdrain region 38. The first drain region 38 at side of the gate 36 isformed, for example, by implanting N type ions into the P substrate 30and the edge portion of the N well 32. The first drain region 38 alsoextends to the shallow trench isolation 40. The first drain region 38also has a salicide layer 52 thereon. A second drain region 42 can beformed by implanting N type ions into the N well 32 and is isolated bythe shallow trench isolations 40 from the first drain region 38.

By performing a salicidation process, salicide layers 46, 52, 56 and 48usually are formed on the source regions 34, the first drain regions 38,the second drain region 42, and the gates 36, respectively. However, aswell known in the prior art, the salicide layer is not formed on asurface of the shallow trench isolation 40, which includes isolationmaterial. As a result, the salicide layer 56 on the second drain region42 is isolated from the salicide layers 52 on the first drain regions 38without using additional photomask.

In the foregoing, the invention particularly uses the shallow trenchisolation to isolate the first drain region 38 and the second drainregion 42.

FIG. 3 shows another embodiment of the invention. In FIG. 3, a crosssectional view of a device structure having a salicide layer isolated bya shallow trench isolation is illustrated. The device structurecomprises an N well 60, a P well 62, a source region 64, a gate 66, afirst drain region 66, a shallow trench isolation 40, and a second drainregion.

The N well 60 is formed in a P type substrate 100. In the N well 60, a Pwell 62 is formed. A gate 66 is formed on the N well 60 other than the Pwell 62. A shallow trench isolation 70 is formed in the P well 62 toisolate the first drain region 68 and the second drain region 72. Thesource region 64 is formed by implanting N ions into the N well 60. Thegate 66 is located between the source region 74 and the first drainregion 68. The first drain region 68 is formed in the N well 60 besidethe gate 66, extending to the shallow trench isolation 70. In addition,a second drain region 72 is formed in the P well 62 and is isolated fromthe first drain region 68 by the shallow trench isolation 70.

By performing a salicidation process, a salicide layer is formed on asurface composed of silicon. The second drain region 72 also has aSalicide layer 82 thereon. That is, salicide layers 76, 82, 86 and 78are formed on the source regions 64, the first drain regions 68, thesecond drain region 72 and the gates 66, respectively. As well known,isolation material is free from forming the salicide layer thereon.Consequently, the salicide layer is not formed on the shallow trenchisolation 70 without using additional photomask. The second drain region72 usually can be formed by implanting P type ions in to the P well 62.

In the foregoing, the invention particularly uses the shallow trenchisolation 70 to isolate the first drain region 68 and the second drainregion 72 without using additional photolithography process, thefabrication coast can be effectively reduced. In this manner, thethermal effect due to the local heat of the drain region is effectivelyreduced. The electric contact on the drain region can remain in anaccepted level.

Other embodiments of the invention will appear to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples to be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

What is claimed is:
 1. A electrostatic discharge (ESD) device with asalicide layer isolated by a shallow trench isolation, comprising: a Ptype substrate; an N well, formed in the P type substrate; a shallowtrench isolation, formed in the N well; a gate structure, on the P typesubstrate other than the N well, wherein the gate structure has a firstside and a second side, and the first side is near to N well; a sourceregion, formed in the P type substrate at the second side of the gatestructure; a first drain region at the first side of the gate structure,formed in the P type substrate and crossing an edge of the N well; asecond drain region, formed in the N well, wherein the second drainregion is isolated from the first drain region by the shallow trenchisolation; and a salicide layer, formed on the gate, the source region,the first and the second drain regions.
 2. The ESD device according toclaim 1, wherein the salicide layer on the second drain region isisolated from the salicide layer on the first drain region by theshallow trench isolation.
 3. An electrostatic discharge (ESD) devicewith a salicide layer isolated by a shallow trench isolation,comprising: a P type substrate; an N well, formed in the substrate; a Pwell, formed in the N well; a shallow trench isolation, formed in the Pwell; a gate structure, formed on the N well other than the P well,wherein the gate structure has a first side and a second side, and thefirst side is near to P well; a source region, formed in the N well atthe second side of the gate structure; a first drain region, at thefirst side of the gate structure, formed in the N well and crossing anedge of the P well; a second drain region, formed in the P well, whereinthe second drain region is isolated from the first drain region by theshallow trench isolation; and a salicide layer, formed on the sourceregion, the first and second drain region, and gate.
 4. The ESD deviceaccording to claim 3, wherein the salicide layer on the second drainregion is isolated from the salicide layer on the first drain region bythe shallow trench isolation.
 5. A salicide layer isolated by a shallowtrench isolation, comprising: a drain region, disposed in a N-wellregion; a shallow trench isolation, partitioning the drain region intotwo parts, wherein the part of the drain region at a first side of agate structure, crosses an edge of the N well region; and a salicidelayer, formed on the two parts of the drain region.